Although the present invention relates generally to signal level translation and, in particular, to processing of differential signals, the invention is hereinafter referenced to instrumentation amplifiers as a primary example of the applicability of this invention. Consequently, the following discussion of prior art or the like pertains to this application as exemplary of an appropriate background of the invention. It is noted in this respect that an instrumentation amplifier is required to provide an output signal that is "N" times the value of an input differential voltage, (V.sub.A -V.sub.B), wherein "N" is a real number. An instrumentation amplifier output voltage is normally not referenced to either of the input signal values V.sub.A or V.sub.B between which the differential voltage exists, but instead, is referenced to a third voltage which may, for example, be a zero or ground voltage. An instrumentation amplifier should respond only to the difference voltage and not to the absolute values of voltages V.sub.A or V.sub.B. The error caused by a shift in the voltages V.sub.A and V.sub.B i.e., common mode rejection ratio, may be limited to about 100 db by the use of good instrumentation amplifiers and this will be seen to produce an output error of 10.sup.-5 volts for a shift of 1 volt in the absolute value of the voltages V.sub.A and V.sub.B. In applications wherein the amplifier is required to process differential signals in the range of 10.sup.-5 volts, it will be seen that a substantial error would be introduced for such a voltage shift.
It is also noted that instrumentation amplifiers are required to present a high impedance at the inputs thereof so that the preceding bridge network or the like will not be loaded by the amplifier. A conventional or typical instrumentation amplifier may employ three operational amplifiers resistively coupled together and this then requires an exact correspondence of particular resistor values in order to preclude the introduction of an additional common mode error. Thus conventional systems employed for instrumentation amplification, for example, must not only employ operational amplifiers that in themselves have low offset voltages and low common mode rejection ratios, but also the resistor network matching must be very precise, in order to preclude the introduction of major errors.
The present invention provides a simple solution to the problems of signal level translation, such as occurs in instrumentation amplifiers by means which may be readily integrated, so as to produce a highly advantageous result.